O01_04

What we still need to learn: lessons from five years operation of the ANSTO in-situ ¹⁴C laboratory

Fulop R¹, SMITH A¹, Yang B¹, White D², Stutz J³, Codilean A⁴, Fink D¹

¹Australia's Nuclear Science and Technology Organisation, Sydney, Australia, ²University of Canberra, Canberra, Australia, ³Victoria University of Wellington, Wellington, New Zealand, ⁴University of Wollongong, Wollongong, Australia

In-situ ¹⁴C is slowly but steadily gaining its place in the cosmogenic nuclide toolkit. The isotope’s relatively short half-life of 5730 years, when compared to the longer-lived and more routinely analysed cosmogenic nuclides, means that it is substantially more sensitive to short term variations in process rates or more suitable at investigating recent exposure events. The above property has proven very valuable in studying deglaciation histories in Antarctica, where the low erosion rates and cold-based glaciation produce widespread inheritance in erratics or bedrock surfaces making it difficult to quantify ice sheet retreat solely with ¹⁰Be. Furthermore, in-situ ¹⁴C used in combination with ²⁶Al and ¹⁰Be is also particularly well suited to studying the relatively short timescales that characterize fluvial sediment transfer and storage, once more illustrated well by recent work.

Despite the above, the extraction of in-situ ¹⁴C from geological samples is still problematic, with recent laboratory intercomparison studies showing considerable overdispersion in both intra and inter laboratory comparisons of standard materials. The discrepancies between laboratories have been attributed to several factors, including the quality of some intercomparison materials, however, clear consensus on the matter is yet to be reached.

We will discuss issues of in-situ ¹⁴C systematics related to phase transformation and micro graphitisation. We will also showcase examples where sample type and quartz impurity have large bearing on success of sample extraction and obtained ¹⁴C results. Lastly, we revisit aspects of in-situ ¹⁴C systematics that still carry considerable uncertainty.